3848 Datasheet, PDF (1/3 Pages) Allegro MicroSystems – DUAL-CONVERSION AM RECEIVER

3848 ³⁸⁴⁸
DUAL-CONVERSION AM RECEIVER
DUAL-CONVERSION AM RECEIVER
Providing the AM signal processing functions for an electronically
T _{FSI 5}
C _{REGULATOR 6 VREG}
U _{AFC OUT 7}
V_CC
SUB
DET
Y _{STOP 8}
D _{L MIX1IN 9}
MIX 1 OUT_A 10
O _{N MIX 1 OUTB 11}
R _{WB AGC 1 IN 12}
P ^O RESET 13
WB
AGC
V _REF
29 _{MIX 2 OUTB}
28 IF
27 AGC (MUTE)
26 _CRYSTAL
25 AGC RATE 2
24 MIX 2 OUT_A
23 _{MIX 2 EB}
22 MIX 2 E _B
21 ^{MIX 2}
BYPASS
ED ^CE _Dwg.PS-012-1
N _{Dwg. No. PS-012-1}
ISCOONRTIRNEUFERE _{ABSOLUTE MAXIMUM RATINGS}
D _{F Supply Voltage, VCC . . . . . . . . . . . . . . 12 V}
Package Power Dissipation, P_D . . . . 1.2 W
— ^{Operating Temperature Range,}
tuned AM receiver (ETR), the A3848EEQ includes two balanced
mixers, a crystal local oscillator, an L/C-tuned local oscillator, oscillator
buffer, IF amplifier, AM detector, scan control detectors, and a switch-
able voltage regulator. This dual-conversion device typically mixes the
incoming RF up to a first IF of 10.7 MHz, then down to 450 kHz, and
then detects the audio. The addition of a JFET matched to a whip
antenna, RF low-pass filter, IF selectivity, and audio stages gives a
complete AM radio which can be used in automotive receivers. The
frequency-detecting stop circuit is also capable of recovering narrow-
band FM, making it useful for scanners or weather band radio applica-
tions. Two AGC and field-strength indicator modes provide special
features for scanning.
The A3848EEQ uses the dual criteria of frequency and amplitude
for establishing a valid stop. Tuning accuracy (frequency criterion) is
established by evaluating phase shift across the detector coil. The
circuitry is similar to that used in FM discriminators. Because this
detection system is phase operated, it remains effective even in the
presence of strong signals, which can cause false stops in systems
using narrow-band filters. The amplitude criterion for stop is deter-
mined by evaluating the IF level. It includes a unique circuit that
removes the effect of the AGC action. This allows the AGC tuning
components to be selected for low-frequency audio performance
without compromising scanning speed.
In the normal AGC mode (AGC RESET low), a slow, narrow-band
field-strength indicator (FSI) is provided for controlling signal-depen-
dent functions such as stereo blending. A fast AGC mode (AGC
RESET high) resets the AGC holding capacitors to maximum gain.
This mode allows cataloging station strengths quickly during a band
sweep.
This AM signal processor is packaged in a rectangular, 32-lead,
plastic, leaded chip carrier (PLCC) for surface-mount applications and
is rated for operation over the temperature range of -40°C to +105°C
are available on special order.
FEATURES
T_A . . . . . . . . . . . . . . . -40°C to +105°C
s Low Noise Figure
s Field-Strength Indicator
Storage Temperature Range,
s Balanced Mixers
s Buffered Oscillator
T_S . . . . . . . . . . . . . . . -65°C to +150°C
s High Dynamic Range First Mixer s Fast Scan Mode
Always order by complete part number: A3848EEQ .